Sleep has been demonstrated to promote the reactivation (replay) and consolidation of important memories and the pruning of irrelevant memories. Consolidation and pruning typically occur during slow wave sleep (i.e., deep sleep), in which memories are transferred from temporary storage in hippocampal regions to long-term storage in neocortical regions. Thus, sleep is vital to daytime cognitive functioning. Nearly all sleep-dependent memory consolidation and pruning research has examined sleep and memory in college-aged adults, thereby ignoring how memory consolidation and pruning may change with normal aging and in clinical sleep disorders. This omission may be particularly crucial because substantial sleep physiology changes (including slow wave sleep declines) and profound memory declines have been reported in healthy older adults and those with mild cognitive impairment and sleep-disordered breathing. The current proposal focuses on this intriguing sleep-memory-aging relationship to determine how age-related sleep changes impact age-related memory changes. Younger adults, healthy older adults, and adults who have mild cognitive impairment as well as sleep-disordered breathing, will encode memories that they are either told will be important in the future or irrelevant in the future, and then they will take a polysomnography-recorded nap. Following the nap, they will be tested on their ability to remember important memories and forget irrelevant memories. Memory performance will be correlated with polysomnography-defined sleep features such as amount of slow wave sleep. The results will shed light on whether sleep-dependent memory consolidation and pruning processes are impaired in healthy older adults and those with clinical sleep disorders. The results will also provide information regarding how the sleep-memory relationship may change from younger adults to older adults; such knowledge can subsequently be used to develop cognitive rehabilitation treatments for healthy older adults, mild cognitive impairment patients, and sleep-disordered breathing patients. For example, if slow wave sleep changes mediate group deficits in memory then a potentially effective treatment might entail prescribing slow wave sleep enhancers. Or, if sleep-disordered breathing events cause memory consolidation/pruning declines then continuous positive airway pressure (CPAP) treatment might be appropriate. Finally, if memory consolidation and/or pruning are relatively preserved during sleep in older adults then a useful intervention may include strategically timed naps during the day. This research will advance knowledge of cognitive aging beyond the waking brain to the exciting new frontier of the sleeping brain.